Doping And Phase Compound Modification Of LiFePO₄ As Cathode Material For Lithium-Ion Batteries

With the rapid development of electronic devices,wide attention has been given to LiFePO₄ due to its low raw material cost,remarkable thermal stability,and environmental friendliness,as it has been rapidly developed into a cathode material for lithium-ion power batteries.However,due to its poor electrical conductivity and low lithium-ion diffusion coefficient,the further development and commercialization of LiFePO₄ has been stalled.Therefore,in this work,with the goal of preparing cathode materials with better electrochemical properties,LiFePO₄ was prepared by using the solvothermal method and made into cells,and on this basis,its electrochemical properties were further enhanced by doping and compounding treatment,meanwhile,the electrochemical properties and modification mechanism of the materials were characterized and analyzed,and the following work was accomplished:（1）LiFePO₄ materials were prepared by the solvent thermal method and modified by doping with Mn for investigating the effects of different doping amounts on the electrochemical properties.With the increase of Mn doping,the electrochemical performance of the cell showed an increasing trend followed by a decreasing trend.The results show that the appropriate amount of Mn doping can improve the initial discharge specific capacity of LiFePO₄.At a doping concentration of 5%,the most effective electrochemical performance is attained when the initial discharge specific capacity reaches 139.7 m Ah/g at a current density of 5 C,with a capacity retention rate of 97.4%after 180 cycles.（2）LiFePO₄ cathode material was co-doped with Mn and K by solvothermal method,and the effect of doping on electrochemical performance and its mechanism were investigated.When the two elements are doped together,the sample shows better ion diffusion dynamics and cycle stability than the blank group or the single doped group.At the current density of 1 C,its initial capacity reaches 159.2 m Ah/g,which remains 97%after 100 cycles,and at the current density of 5 C,its capacity reaches 145m Ah/g,which remains 94%after 400 cycles.（3）A two-step solvothermal method was used to wrap defect-rich structured vanadium oxides in the outer layer of LiFePO₄ nanoparticles.Vanadium oxide with oxygen vacancy inside has better conductivity than pure phase.After analyzing the structure of defective vanadium oxide,its modification mechanism was analyzed.When it is coated in the outer layer of LiFePO₄,the composite modified group shows better cycle life and conductivity than the blank group.At the current density of 5C,the modified group showed a high capacity of 138.86 m Ah/g,which can still maintain133.7 m Ah/g after 500 cycles,and the capacity retention rate reached 95%.（4）A few-layers MXene material with HF etching and intercalation stripping were compounded with LiFePO₄ by solvothermal method to obtain a cathode material with excellent electrochemical performance.Because MXene has good conductivity and its surface is rich in active functional groups,LiFePO₄ can be effectively combined with it to obtain excellent conductivity and magnification performance.At a current density of 5 C,its capacity is up to 153.12 m Ah/g,and it still maintains 95%of its initial capacity after 1000 cycles.